LP 890-9, also known asSPECULOOS-2 orTOI-4306, is a high proper motionred dwarf star located 105light-years (32 pc) away from theSolar System in the constellation ofEridanus. The star has 12% the mass and 15% the radius of theSun, and a temperature of 2,871 K (2,598 °C; 4,708 °F). It is extremely faint and, with anapparent magnitude of 18, is the faintest star with exoplanets discovered by theTransiting Exoplanet Survey Satellite.[6]
In 2022, twoexoplanets were discovered in orbit around this star. The first planet, LP 890-9 b, was initially identified usingTESS. Further observations usingSPECULOOS confirmed this planet and discovered a second planet, LP 890-9 c. Both planets are likelyterrestrial planets, somewhat larger than Earth. The outer planet LP 890-9 c orbits within thehabitable zone, and is a favorable target for atmospheric characterization usingJWST.[3][7]
LP 890-9 c orbits near the inner edge of the conservative habitable zone, and models differ as to whether the planet is more likely to resembleEarth orVenus. Spectra from JWST should make it possible to distinguish between these two scenarios.[4] The planet istidally locked to its host, meaning it has noday-night cycle like Earth.[8] While the planet's location in thehabitable zone suggests a strong possibility of an Earth-like atmosphere and climate, the planet's large size may count against its habitability. In addition, the planet is close enough to its star that the powerfulradiation may reduce its chances of habitability.[9] Another challenge for the potential habitability of LP 890-9 c is the magma ocean that would have formed during its infancy, which may have lasted for up to 50 million years. This could have removed eight Earth oceans’ worth ofwater and left 2000 bars ofoxygen in its atmosphere, although if its initialhydrogen envelope had 0.1 Earth masses, no water would have been lost. Furthermore, the circulation of the planets orbit would take about 7 billion years, producing hundreds of terawatts oftidal heating.[10]
The habitability of LP 890-9 c depends heavily on the initialvolatile content and properties and the planet is unlikely to supportlife.[10]
| Companion (in order from star) | Mass | Semimajor axis (AU) | Orbital period (days) | Eccentricity | Inclination | Radius |
|---|---|---|---|---|---|---|
| b | <13.2 M🜨 | 0.01875±0.00010 | 2.7299025+0.0000034 −0.0000040 | — | 89.67+0.22 −0.33° | 1.320+0.053 −0.027 R🜨 |
| c | <25.3 M🜨 | 0.03984±0.00022 | 8.457463±0.000024 | — | 89.287+0.026 −0.047° | 1.367+0.055 −0.039 R🜨 |
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